<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>:only-of-type</title>
    <style>
    h1:only-of-type {
        color: brown;
    }
    p:only-of-type {
        color: aquamarine
    }
    </style>
</head>
<body>
    <h1>:only-of-type</h1>
    <p>代表任意一个元素，这个元素没有其它相同的兄弟元素</p>
    <p></p>

    <a href="https://developer.mozilla.org/zh-CN/docs/Web/CSS/:only-of-type">:only-of-type</a>
</body>
</html>
